Fair point, bookgrl.
I think Jim's analogy of the job interview doesn't add up - if there were to be an "interview" to assess attitude, it should take place prior to the Citizenship Invitation. Once invited, the decision has been made.
I think it's more like one's attitude at a registry office wedding - to my knowledge, as long as people comply with the requirements, they can't be turned away from getting married because the officiant doesn't like something about them, so again, I disagree with Jim's suggestion.
If there were a dress code for the citizenship ceremony that people were violating, that would be one thing, but there is no dress code. Even in posh restaurants where men don't bring a suitable jacket, some of the restaurants offer a loaner jacket, and something like that would only be fair if a dress code were to be imposed for the citizenship ceremony.
I am old enough to remember when people dressed up for church (based on my own churchgoing experiences), and as well to see over the years that people started wearing whatever they wanted - some continued to dress up, and some didn't. It's just a sign of the times, IMO.